FTIR Analysis of Microplastics: How FTIR Is Used for Microplastic Identification
FTIR analysis of microplastics is a widely used analytical approach for identifying the polymer composition of microplastic particles. By measuring the infrared absorption characteristics of a particle and comparing its spectrum with reference spectra, researchers can determine whether a microplastic is made from polymers such as polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polyvinyl chloride (PVC), or other materials.
For laboratories working on water quality, environmental monitoring, wastewater, sediment, and plastic pollution research, FTIR for microplastics provides molecular-level information that cannot be obtained reliably through visual inspection alone. However, FTIR is not the only technology available for microplastic analysis. Raman spectroscopy provides another molecular fingerprinting approach and can offer advantages for certain particle sizes, colors, and sample conditions.
What Is FTIR Analysis of Microplastics?
FTIR analysis of microplastics uses Fourier Transform Infrared Spectroscopy to identify the chemical structure of individual plastic particles.
Different polymers absorb infrared radiation at characteristic wavenumbers because their molecular bonds vibrate differently. The resulting FTIR spectrum acts as a molecular fingerprint. By comparing the measured spectrum with a reference spectral library, the polymer type can be assigned.
For example, FTIR can be used to distinguish common microplastic polymers including:
- Polyethylene (PE)
- Polypropylene (PP)
- Polystyrene (PS)
- Polyethylene terephthalate (PET)
- Polyvinyl chloride (PVC)
- Polyamide (PA/Nylon)
Research has demonstrated that FTIR and micro-FTIR can identify common microplastic polymers through characteristic spectral patterns and library matching.
For laboratories that need to analyze large numbers of particles, however, the challenge is not simply identifying one plastic particle. The bigger challenge is efficiently locating, measuring, identifying, classifying, and reporting hundreds or thousands of particles.
This is where automated microplastic analysis becomes important.
How Does FTIR for Microplastics Work?
A typical FTIR for microplastics workflow includes several steps:
- Sample collection
- Sample preparation
- Filtration or particle separation
- Particle observation
- FTIR spectral acquisition
- Spectral processing
- Reference-library matching
- Polymer identification
- Data analysis and reporting
The FTIR spectrum of a particle is compared with reference spectra. A sufficiently strong spectral match can provide evidence for the polymer identity.
The analytical workflow is important because environmental samples rarely contain clean plastic particles alone. Organic matter, minerals, pigments, additives, biofilms, and other substances can interfere with spectral identification. Research has shown that co-existing substances can increase uncertainty in microplastic identification.
Therefore, FTIR microplastic analysis should not be considered simply a process of “putting plastic into an FTIR instrument.” Sample preparation, particle selection, measurement conditions, spectral quality, reference libraries, and matching criteria all influence the final result.
What Can Microplastic FTIR Analysis Identify?
The main purpose of microplastic FTIR analysis is polymer identification.
A particle that looks like plastic under a microscope cannot always be reliably classified by appearance alone. Color, shape, transparency, and surface morphology can provide useful preliminary information, but chemical identification requires a spectroscopic or other analytical method.
FTIR can provide molecular information for common polymers such as PE, PP, PET, PS, PVC, and nylon. Studies using micro-FTIR have also developed validated identification procedures for common environmental microplastics.
FTIR analysis can therefore help answer questions such as:
What type of plastic is this particle?
Is the particle actually a polymer?
Is the sample dominated by PE, PP, PET, PS, PVC, or another polymer?
How does the polymer composition differ between environmental samples?
These questions are important for environmental monitoring, pollution-source investigation, wastewater research, and microplastic research.
FTIR vs. Raman for Microplastic Analysis
FTIR and Raman spectroscopy are both molecular spectroscopy techniques, but they are not identical.
FTIR microplastic analysis detects infrared absorption associated with molecular vibrations, while Raman spectroscopy measures changes in molecular polarizability associated with Raman scattering.
Both techniques can provide molecular fingerprints for polymer identification, but their practical performance can differ depending on particle size, color, fluorescence, sample preparation, and measurement configuration.
FTIR is a well-established method for microplastic identification and has been extensively studied for environmental samples. Micro-FTIR can extend analysis to smaller particles than conventional ATR-FTIR, although the practical particle-size range depends on the instrument configuration and measurement mode.
Raman spectroscopy can also identify microplastic polymers and can be particularly useful when smaller particles or wet samples are involved. Recent research continues to compare FTIR and Raman-based approaches with other optical technologies for high-throughput microplastic classification.
Therefore, the best technology depends on the actual analytical requirement rather than simply choosing the most popular technique.
Why Automated Microplastic Analysis Matters
Traditional microplastic analysis can involve a large amount of repetitive manual work.
Researchers may need to:
- Locate individual particles under a microscope
- Record particle coordinates
- Measure particle size
- Classify particle morphology
- Select particles for spectroscopy
- Acquire spectra
- Match spectra with a database
- Recheck uncertain particles
- Organize analytical results
- Generate reports
When the number of particles increases, manual operation becomes a major limitation.
For this reason, automation is becoming increasingly important in microplastic analysis.
AIMOLI AML518 Automatic Microplastic Analyzer
For laboratories that need higher-throughput microplastic identification, AIMOLI AML518 Automatic Microplastic Analyzer for Water provides an automated alternative to highly manual microplastic workflows.
According to AIMOLI, the AML518 integrates microscopy and Raman spectroscopy and is designed specifically for automated microplastic identification and characterization in water samples. The system supports microplastic particles from approximately 300 μm to 5000 μm and uses dual 785 nm and 1064 nm laser sources to help address fluorescence interference.
Unlike a conventional manual FTIR for microplastics workflow, AML518 is designed around automation. The system combines sample handling, microscopic imaging, spectral identification, verification, and reporting into an integrated workflow.
Its automated process includes:
- Sample pretreatment
- Automated slide loading and unloading
- Automatic microscope focusing
- Particle imaging
- Particle coordinate and size recording
- Raman spectral acquisition
- Automated spectral database matching
- Suspected-particle verification
- Automatic report generation
AIMOLI states that the AML518 can accommodate 10–20 microscope slides, operate continuously for 24 hours, and provide automated processing designed to improve efficiency compared with manual workflows.
For laboratories analyzing large numbers of water samples, this automation can be more important than simply increasing the speed of one spectral measurement.
FTIR Microplastic Analysis or Raman Microplastic Analysis?
The choice between FTIR microplastic analysis and Raman-based microplastic analysis should be based on the analytical objective.
| Requirement | FTIR / Micro-FTIR | Raman / AML518 |
|---|---|---|
| Polymer identification | Yes | Yes |
| Molecular fingerprinting | Yes | Yes |
| Microplastic research | Yes | Yes |
| Automated particle workflow | Depends on system | AML518 is designed for automation |
| Microscopic particle mapping | Depends on system | Integrated |
| Automated particle verification | Depends on system | Supported |
| Automated report generation | Depends on system | Supported |
| Water microplastic analysis | Yes | Yes |
| Large-scale automated workflow | System-dependent | AML518 focuses on automation |
FTIR remains an important technology for microplastic FTIR analysis, particularly when established FTIR or micro-FTIR laboratory workflows are already available. At the same time, Raman-based systems can provide a different route to automated microplastic identification.
For laboratories that prioritize automated analysis, continuous operation, particle imaging, spectral identification, and automatic reporting, AIMOLI AML518 is worth evaluating as an alternative technology.
Can FTIR Identify Very Small Microplastics?
The answer depends on the FTIR configuration.
Conventional FTIR with ATR accessories is generally more suitable for larger particles or bulk polymer characterization, while micro-FTIR provides microscopic analysis capabilities for smaller particles. Published research has reported micro-FTIR applications reaching particles around the micrometer scale, depending on the instrument and measurement configuration.
This distinction is important when discussing FTIR analysis of microplastics. “FTIR” is not a single instrument configuration, and the achievable particle size depends on optical resolution, measurement mode, sample preparation, particle properties, and instrument design.
For smaller particles, laboratories should evaluate the complete analytical system rather than comparing FTIR and Raman solely by the name of the technology.
Why Spectral Libraries Are Important in Microplastic FTIR Analysis
A spectrum by itself does not automatically provide the polymer name.
In microplastic FTIR analysis, the measured spectrum is normally compared with reference spectra. The quality and relevance of the spectral library therefore directly affect polymer identification.
A reliable workflow should consider:
- Reference polymer spectra
- Spectral quality
- Background correction
- Baseline correction
- Noise
- Spectral range
- Matching algorithm
- Match threshold
- Interference from environmental materials
Validated micro-ATR-FTIR research has shown that defined spectral requirements, processing methods, matching algorithms, and identification thresholds can improve the reliability of polymer identification.
This is particularly important when analyzing environmental samples rather than clean laboratory plastics.
What Is the Best Method for Microplastic Analysis?
There is no single analytical technology that is optimal for every microplastic application.
FTIR for microplastics is a mature and widely used approach for polymer identification. Micro-FTIR extends the method to smaller particles and can be integrated with microscopic particle analysis.
Raman spectroscopy provides another molecular identification approach and can be advantageous for specific sample types and automated workflows.
For laboratories that need to process large numbers of water samples, the key question should therefore be:
Do you need a manual spectroscopy method, or do you need an automated microplastic analysis workflow?
If the priority is automated particle imaging, identification, verification, and reporting, the AIMOLI AML518 Automatic Microplastic Analyzer is a practical system to consider.
Conclusion
FTIR analysis of microplastics is an established method for identifying polymer composition through infrared spectral fingerprints. FTIR for microplastics is particularly useful when researchers need chemical confirmation beyond visual particle classification.
However, microplastic analysis is not only a spectroscopy problem. Large-scale environmental monitoring also requires efficient particle detection, imaging, identification, verification, data management, and reporting.
For laboratories looking beyond traditional manual FTIR microplastic analysis, AIMOLI’s AML518 Automatic Microplastic Analyzer combines microscopy, Raman spectroscopy, automated particle handling, spectral identification, verification, and report generation into one workflow. This makes it a solution worth considering for laboratories that need to improve the efficiency and automation of water microplastic analysis.
FAQ: FTIR Analysis of Microplastics
What is FTIR analysis of microplastics?
FTIR analysis of microplastics uses Fourier Transform Infrared Spectroscopy to identify the polymer composition of microplastic particles by comparing their infrared spectra with reference spectra.
What is FTIR used for in microplastic analysis?
FTIR for microplastics is mainly used for polymer identification and chemical characterization. It can help distinguish polymers such as PE, PP, PET, PS, PVC, and nylon.
Is FTIR better than Raman for microplastics?
Neither technology is universally better. FTIR is a well-established method for polymer identification, while Raman can provide advantages for certain particle sizes, sample conditions, and automated workflows. The best choice depends on the sample and analytical requirements.
Can FTIR detect microplastics smaller than 10 μm?
Micro-FTIR can analyze particles at the micrometer scale, but the practical detection and identification limit depends on the instrument configuration, optical system, measurement mode, particle properties, and sample preparation.
What is the difference between FTIR and micro-FTIR?
FTIR is the broader infrared spectroscopy technique. Micro-FTIR combines FTIR spectroscopy with microscopic analysis, allowing researchers to target and analyze much smaller individual particles.
What is AIMOLI AML518?
AIMOLI AML518 is an automatic microplastic analyzer designed for water samples. It combines microscopy and Raman spectroscopy with automated sample handling, particle imaging, spectral identification, verification, and report generation.
Is AML518 an FTIR microplastic analyzer?
No. AML518 is a Raman-based automatic microplastic analyzer, not an FTIR instrument. It is designed as an alternative analytical approach for automated microplastic identification and characterization. AIMOLI states that AML518 supports particles from approximately 300 μm to 5000 μm and uses 785 nm and 1064 nm dual-laser Raman technology.
Which method should a laboratory choose?
If the laboratory already has an established FTIR or micro-FTIR workflow, FTIR can be an effective choice for polymer identification. If the laboratory needs a more integrated automated workflow for particle imaging, identification, verification, and reporting, AIMOLI AML518 can be considered as a Raman-based automated solution.
